This invention broadly relates to a non-cooling type infrared ray sensor of a bolometer type. More specifically, this invention is directed to an infrared ray sensor in which a temperature is varied by absorbing an incident light ray of an infrared ray and a signal of a radiation intensity of the infrared ray is read-out by varying an electrical resistance value in dependency upon the temperature variation.
The bolometer utilizes temperature variation of an electrical resistance value of metal or a semiconductor thin-film, which is thermally insulated from a substrate material.
In general, when temperature coefficient of the electrical resistance (TCR) of the material for the bolometer becomes high, temperature resolution (NETD) of the infrared ray sensor becomes low, thus improving sensitivity.
An alloy thin-film such as a nickel iron alloy has low TCR of about 0.5%. In consequence, it is considered that a conductive oxide thin-film such as a vanadium oxide thin-film, a perovskite type Mn oxide film, and a YBa2Cu3Ox thin-film is advantageous as a resistive film for the bolometer for use in the infrared ray sensor with high sensitivity.
This reason will be explained as follows.
These conductive oxide thin-films represents excessively high TCR of about 2%/K in the vanadium oxide thin-film, about 2xcx9c5%/K in the YBa2Cu3Ox thin-film. Further, the conductive oxide thin film represents extremely high TCR of 5%/K or higher, particularly exceeding 10%/K in the perovskite type Mn oxide by utilizing phase transition between an insulator and a metal caused by magnetic phase transition inherent to such material.
Referring now to FIG. 1, description will be hereinafter made about the structure of the infrared ray sensor in which the oxide thin-film is used as the resistive element for the bolometer in the related art.
In FIG. 1, the reference numeral 1 represents a Si substrate, the reference numeral 2 represents a bridge structure body, a reference numeral 3 represents a space, the reference numeral 4 represents a resistive element for the bolometer, the reference numeral 5 represents a wiring pattern, and a reference numeral represents an infrared ray reflection film.
As illustrated in FIG. 1, the infrared sensor of the bolometer type generally has such a micro-bridge structure that the resistive element 4 for the bolometer is insulated from the Si substrate 1 via the space 3.
To this end, the resistive element 4 for the bolometer can be thermally insulated from the silicon substrate 1. Under such a circumstance, the oxide thin-film selected from the above films is used as the resistive elements for the bolometer.
With this structure, when the infrared ray is entered to a cell, a part thereof is initially absorbed by the infrared ray absorption film 7, and the infrared ray, which is partially transmitted, is reflected by the infrared ray reflection film 8. A resultant infrared ray is completely absorbed by the infrared ray absorption film 7. The absorbed infrared ray generates heat, and heats a diaphragm to thereby vary the electrical resistance of the resistive element 4 for the bolometer.
Then, a signal is detected by a read-out circuit formed in the Si substrate 1 via the wiring pattern 5 connected to the Si substrate 1 through a supporting portion of the bridge structure body 2 from the both ends of the resistive element 4 for the bolometer.
Subsequently, a process for manufacturing the aforementioned infrared ray sensor will be explained as follows.
Initially, metal with infrared reflection rate such as WSi is deposited on the Si substrate 1 with the read-out circuit by the sputtering method to thereby form the infrared reflection film 8.
Then, a sacrifice layer is formed at the position of the space, which will be formed later, on the infrared ray reflection film 8 by the use of a polysilicon film or the like. Herein, it should be noted that the polysilicon film may be deposited by CVD method.
An insulating film such as SIN and SiO2 is deposited on the sacrifice layer by the plasma CVD method, thereby forming the bridge structure body 2. Next, the metal with low thermal conductivity such as Ti is formed on the bridge structure body 2 by the sputtering method, is exposed, is developed and is etched to thereby form the wiring pattern 5.
Successively, the oxide thin-film serving as the resistive element 4 for the bolometer such as a vanadium oxide thin-film, a perovskite type Mn oxide film, and a YBa2Cu3Ox thin film is deposited by the sputtering method. The resistive element for the bolometer is also formed by the development and etching process like the above wiring pattern.
The insulating film such as SiO2 is deposited on the bridge structure body 2 including the resistive element by the plasma CVD method in order to protect the resistive element 4 for the bolometer, thus forming the protection film 6.
Further, the infrared ray absorption film 7 such as TiN is deposited on the protection film 6 by the use of the reactive sputtering method.
Finally, the sacrifice layer is wet-etched by hydrazine to form the space 3. Through aforementioned multiple steps, such a diaphragm that the portion including the resistive element 4 for the bolometer is floated is completed.
By adopting such a structure, it is difficult that heat of the infrared ray absorbed by the infrared ray absorption film 7 is escaped to an external portion. Thereby the heat is efficiently utilized to raise up the temperature of the resistive element 4 for the bolometer
As discussed above, the non-cooling type infrared ray sensor of the bolometer type can effectively detect the infrared ray by forming the diaphragm of such a structure that the portion including the resistive element 4 for the bolometer is floating.
The non-cooling type infrared sensor is advantageous in low price in addition to operability with respect to a shape and a weight in comparison with the cooling type infrared sensor. However, the conventional non-cooling type infrared ray sensor is produced by using an excessively complex production process.
For example, paying attention for a deposition process, the infrared ray reflection film 8, the resistive element 4 for the bolometer, the wiring pattern 5, and the infrared ray absorption layer 7 are deposited by the sputtering method. Further, the sacrifice layer such as the polysilicon film, the bridge structure body 2, and the protection film 6 are formed by the use of the CVD method.
Moreover, many production steps such as a resist applying step, a drying step, an exposing step, a developing step, a resist removing step, and a washing step are required for formation of each layer such as the wiring pattern 5 and the resistive element 4 for the bolometer.
In the conventional production process, a vapor deposition process with high cost is carried out many times, and a plurality of steps are necessary in the patterning, thus increasing the production cost.
Accordingly, if the vapor deposition process or the patterning step can be reduced, the production cost will be lowered, thereby providing the non-cooling type infrared ray sensor with lower cost.
In addition, the deposition temperature of the resistive element 4 for the bolometer occurs problems during manufacturing the non-cooling type infrared ray sensor of the bolometer type. This is because the resistive element 4 for the bolometer is formed on the Si substrate 1 with the signal read-out circuit via the space 3 for thermally insulating, as discussed above.
Further, it is required that the deposition temperature is low at 400xcx9c500xc2x0 C. not to destroy the signal read-out circuit formed in the Si substrate. Moreover, it is also impossible to utilize a physical etching method such as ion milling during forming the pattern of the resistive element 4 for the bolometer. This is because the Si signal read-out circuit formed on an under layer is damaged by the physical etching.
Thus, it is particularly required that the conductive oxide thin-film used for the resistive element 4 for the bolometer has consistency with the Si production process in addition to high TCR. From the viewpoint of the production process, vanadium oxide is most suitable material among the above-mentioned materials.
This is because the annealing temperature is low at 400xcx9c550xc2x0 C. during forming the vanadium oxide thin-film, as disclosed in Japanese Unexamined Patent Publication (JP-A) No. 2000-143243. Further, the thin-film has such an advantage that the patterning can be performed by the reactive ion etching instead of the physical etching.
However, the TCR of the vanadium oxide thin-film is equal to about 2%/K. As a result, it is insufficient with respect to material to achieve high sensitivity of the non-cooling type infrared ray sensor in the future.
To realize the non-cooling type infrared ray sensor with higher sensitivity, the YBa2Cu3Ox thin film or the perovskite type Mn oxide each having higher TCR is more advantageous. However, the high deposition temperature about 1000xc2x0 C. in the case of the sol-gel method and 700xc2x0 C. or higher in the case of the sputtering is necessary to realized that these thin-films have high TCR.
As long as such a high deposition temperature is necessary, it is difficult to apply even an attractive thin-film with high TCR for the production process of the infrared sensor. Further, the reactive ion etching can not be applied to form the resistive element for the bolometer by patterning the YBa2Cu3 Ox thin-film or the perovskite type Mn oxide.
Consequently, the physical etching method such as the ion milling must be used. In this point, it is considered to be difficult to apply these thin-films for the resistive film 4 for bolometer of the infrared ray sensor.
Thus, although the vanadium oxide, the YBa2Cu3Ox thin-film or the perovskite type Mn oxide is desirable as the resistive film 4 for the bolometer of the infrared ray sensor, they have problems regarding the production process with respect to the performance and the conventional production method.
It is therefore an object of this invention to provide a method for manufacturing an infrared ray sensor which is simple in a production process in a non-cooling infrared ray sensor of a bolometer type which is cheap in a production cost with high sensitivity.
According to a first aspect of this invention, in an infrared ray sensor for a bolometer, a temperature is varied by absorbing an incident light ray of an infrared ray, and a signal of radiation intensity of the infrared ray is read-out by changing an electrical resistance value in dependency upon temperature variation.
Under this circumstance, a bridge structure body, a resistive element film for the bolometer, and a protection film is formed via a space on a substrate. Herein, the protection film is placed on a surface including the resistive element film.
Then, the bridge structure body, the resistive element film and the protection film is formed into a solution form by dissolving metal organic compound into solvent.
Next, the solution is applied and dried.
Subsequently, a laser ray is irradiated for the solution with wavelength of 400 nm or less.
Finally, a bond between carbon and oxygen is decomposed and cut to thereby form an oxide thin-film.
According to a second aspect of this invention, the resistive element film is at least one selected from the group consisting of a vanadium oxide thin-film, a perovskite type manganese oxide thin-film, and YBa2Cu3Ox.
According to a third aspect of this invention, the bridge structure body is at least one selected from the group consisting of a SiO2 thin-film, and TiO2 thin-film, and an Al2O3 thin-film.
According to a fourth aspect of this invention, the protection layer is at least one selected from the group consisting of an SiO2 thin-film, an TiO2 thin-film, and an Al2O3 thin-film.
According to a fifth aspect of this invention, the laser light ray with wavelength of 400 nm or less is at least one excimer laser ray selected from the group consisting of ArF, KrF, XeCl, XeF, and F2.
According to a sixth aspect of this invention, the laser ray with wavelength of 400 nm or less is irradiated with multiple stages.
According to a seventh aspect of this invention, the laser ray is irradiated not to completely decompose the metal organic compound in an first stage, and the laser ray is irradiated to crystallize the oxide or to form the oxide into an amorphous form in a subsequent stage.
According to an eighth aspect of this invention, the substrate applied with the metal organic compound is heated to 500xc2x0 C. to or less during irradiating the laser ray with the wavelength of 400 nm or less.
According to a ninth aspect of this invention, the metal organic compound comprises metal organic acid salt.
According to a tenth aspect of this invention, metal of the metal organic acid salt is at least one selected from the group consisting of V, La, Nd, Pr, Ca, Sr, Ba, Mn, Y, Cu, Si, Ti, and Al.
According to an eleventh aspect of this invention, organic acid of the metal organic acid salt is at least one selected from the group consisting of naphthenic acid, 2-ethyl hexanoic acid, caprylic acid, stearic acid, lauric acid, acetic acid, propionic acid, oxalic acid, citric acid, lactic acid, benzonic, salicylic acid, and ethylenediaminetetraacetic acid.
According to a twelfth aspect of this invention, the metal organic compound comprises metal acetylacetonato complex.
According to a thirteenth aspect of this invention, the metal acetylacetonato complex is at least one selected from the group consisting of V, La, Nd, Pr, Ca, Sr, Ba, Mn, Y, Cu, Si, Ti, and Al.
According to a fourteenth aspect of this invention, solvent for dissolving the metal acetylacetonato complex is at least one selected from the group consisting of butyl acetate, toluene, acetylacetone, and methanol.
According to this invention, the vapor deposition process or the exposing step, the developing step, and the etching step can be reduced by adopting the optical reaction process using the laser ray during forming the oxide thin-film. Thereby, it is possible to provide the non-cooling type infrared my sensor with low cost.